Lay the beef in a large roasting pan with the bone side down. (The ribs act as a natural roasting rack.) In a small bowl mash together the garlic, horseradish, rosemary, thyme, salt, pepper, and olive oil to make a paste. Massage the paste generously over the entire roast. Put the pan in the oven and roast the beef until the internal temperature of the meat registers 125 degrees F on an instant-read thermometer (medium-rare), 1 1/2 to 2 hours. Remove the beef to a carving board and let it rest for 20 minutes before carving.

Pour off some of the pan drippings and place pan on stovetop over medium-high heat.

Add the white wine and bring to a simmer, scraping the bits on the bottom of the pan. Reduce the wine by half. Whisk in the flour, then add the broth and continue to cook, whisking until sauce thickens into a gravy, about 10 minutes.